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2 HUMAN FUNCTIONAL ANATOMY 213 THE UPPER LIMB EARLY LIMB DEVELOPMENT IN THE FISH (or early human embryo) Slight elevations of ectoderm appear in lateral plate (4th week). Apical ectodermal ridge induces proliferation of limb mesenchyme. Dorsal and ventral muscle masses connect the girdle to the limb bud. Limb girdle in body wall Proximal, middle and distal segments of the limb THIS WEEKS LAB: Proximal parts, plexuses and patterns READINGS Stern. Essentials of Gross anatomy – The upper limb Stern. Core concepts in Anatomy:- 80: Organization of upper limb musculature and the brachial plexus Faiz and Moffat. Anatomy at a Glance:- Nerves of the Upper limb 1 & 2 (parts 30 &31) Grant's Method:- Upper limb and Back (especially pectoral region and axilla) OR any other regional textbook - similar sections IN THIS LECTURE I WILL COVER: Ontogeny and Phylogeny The Pectoral fin The primitive tetrapod forelimb Rotations of the limb in phylogeny Dorsal and ventral muscle/nerve/girdle bone Segmental nerve supply and muscle groups Brachial plexus The fin, or paddle has: Preaxial and postaxial borders (front and back edges) Dorsal and ventral surfaces (top and bottom) Dorsal muscles elevate the fin. Attach to dorsal elements of the girdle (“scapula” and vertebrae) Ventral muscles depress the fin. Attach to ventral elements of the girdle (coracoid) Muscle groups of the upper limb 3 PRIMITIVE TETRAPOD FORELIMB The characteristic segments of the limb (shoulder, arm, forearm, & hand) Were present in the fins of fossil fish But became fully developed in terrestrial forms (amphibia & reptiles) The orientation of the limb is still the same: Dorsal is dorsal and Ventral is ventral Pre-axial (thumb side) is front edge of limb The limbs and mode of locomotion are very similar in fish & reptiles 4 MAMMALIAN FORELIMB ROTATIONS 90 degrees LATERAL ROTATION The preaxial border (thumb side) becomes dorsal This brings the dorsal muscles to the posterior aspect of the limb and the ventral muscles to the anterior aspect 5 6 MAMMALIAN FORELIMB ROTATIONS 90 degrees ADDUCTION DORSAL AND VENTRAL MUSCLES The limb rotations modify the action of the muscles Primitive dorsal elevators and ventral depressors of the fin Become dorsal extensors, and ventral flexors of the limb Adduction brings the limb under the trunk. (Classic mammalian posture) Preaxial border (thumb side) becomes lateral Dorsal muscles remain on the posterior aspect of the limb Dorsal muscles either: Attach to the vertebral column or the true scapula or Lie in dorsal compartments of the limb Ventral muscles either: Attach to the coracoid part of the scapula, clavicle, ribs or sternum or Lie in ventral compartments of the limb Quadrupedal animals pronate their forearm that the digits face forwards so In humans the limb stays in the same orientation, but we stand on our hindlimbs and the upper limb hangs at our side (90 degrees extension) 7 Dorsal and Ventral MUSCLE COMPARTMENTS OF THE UPPER LIMB And their Dorsal and Ventral nerves Ventral: Musculocutaneous nerve (C56) Anterior compartment of the arm 8 BRACHIAL PLEXUS TRUE LIMB MUSCLES ATTACH TO LONG BONES OF THE LIMB The brachial plexus supplies all these muscles. This excludes muscles attaching the axial skeleton to the scapula. These muscles are derived from cranial or cervical myotomes Eg. Trapezius and sternomastoid - Accessory nerve CN 11 Serratus anterior, rhomboids, levator scapulae - C3,4,5,6 C5 Dorsal: Radial nerve (C5678T1) C6 C7 C8 T1 ROOTS Posterior compartment of the arm TRUNKS Upper Middle Lower Ventral: Median nerve C5678T1 Anterior compartment of the forearm DIVISIONS Anterior and posterior for each trunk Dorsal: Radial nerve (C5678T1) CORDS Lateral Posterior Medial Posterior compartment of the forearm Ventral: NERVES Musculocutaneous Median Ulnar nerve (C8T1) Hand Axillary Radial Ulnar 9 BRACHIAL PLEXUS 10 MUSCLE COMPARTMENTS OF THE UPPER LIMB Basis of the brachial plexus Compartment Anterior shoulder Ventral Segments C5 & C6 Nerve Pectoral nerves Posterior shoulder Dorsal C5 & C6 Axillary Suprascapular Subscapular & thoracodorsal Anterior arm Ventral C6 & Musculocutaneous Posterior arm Dorsal C6 & Radial nerve Posterior forearm Ventral C7 & Radial nerve Anterior forearm Ventral C7 & Median (and ulnar) nerves Hand Ventral C8 & T1 Ulnar (and median) nerve The brachial plexus is how the nerves of the upper limb are formed. You can see the need for a plexus, otherwise there would be a mess of tiny nerves. 11 “ONTOGENY RECAPITULATES PHYLOGENY” Ernst Haeckel Ontogeny = The development of the individual Phylogeny = Evolution of the species The development of the individual recapitulates the evolution of the species Classic example is the Development of the frog. Retracing the evolution of vertebrates from fish to reptiles From the tadpole stage (like a fish) 1. 2. 3. 4. 5. Water breathing creature with tail and no limbs Rudimentary limbs Reduction of tail Breathes air Fully developed limbs,, loss of tail, becomes a land animal. To the fully developed frog I WANT TO TRACE THE DEVELOPMENT OF THE LIMBS IN VERTEBRATES AND COMPARE IT TO THE GROWTH OF LIMBS IN THE INDIVIDUAL